Theoretical Analysis of Non-Orthogonal Multiple Access Schemes for Spectral Efficiency Improvement in Nigerian Mobile Networks

Non-orthogonal multiple access enables simultaneous service of multiple users on the same time-frequency resource through superposition coding at the transmitter and successive interference cancellation at the receiver, offering fundamental spectral efficiency advantages over orthogonal schemes at the cost of increased receiver complexity. The theoretical performance limits of NOMA under the propagation and interference conditions of Nigerian mobile networks have not been analytically characterized, limiting its evaluation as a candidate enhancement for Nigerian 5G deployments. This doctoral study conducts a rigorous theoretical analysis of NOMA schemes for spectral efficiency improvement in Nigerian mobile networks, deriving original analytical expressions for system capacity, outage probability, and fairness metrics under channel models parameterized by propagation measurements in Ibadan, Kaduna, and Maiduguri. An original paired NOMA user selection strategy exploiting the statistical structure of the measured Nigerian urban channel distributions is proposed and analytically evaluated. Closed-form expressions for outage probability of both near and far NOMA users are derived, incorporating the imperfect successive interference cancellation residual error model. Theoretical analysis demonstrates that the proposed selection strategy achieves a sum capacity improvement of 43% over conventional orthogonal multiple access under low and medium SNR conditions representative of cell edge users in measured environments. Stability analysis of the derived outage probability expressions under seasonal channel variation patterns observed in northern Nigerian measurements is conducted, providing robustness characterization essential for deployment confidence. The doctoral study contributes new analytical tools for NOMA system design applicable to the propagation characteristics of West African mobile network environments. Keywords: NOMA, spectral efficiency, successive interference cancellation, outage probability, Nigeria.